Those ratios are the length of the auditorium divided by the width of the screen.
I like to specify viewing distance as the number of "picture heights" you are viewing the movie from. Standard SMPTE 196M specifies a preferred viewing distance of 2 to 4 picture heights for 35mm film. So for a screen that is 20 feet high with adjustable side masking, you would have a 20 x 48 foot "scope" image, and a 20 x 37 foot "flat" (1.85:1) image, and the "best seats in the house" would be between 40 and 80 feet from the screen. A well made 35mm film with "Film Done Right" presentation will probably look pretty good anywhere between 1 and 5 screen heights distance. Any closer than 1 screen height, and you're constantly turning your head to follow the action, and the graininess becomes noticeable. IMHO, any further than about 5 screen heights, and you might as well be watching television, although some people like the back seats for more privacy.
Large formats like 70mm permit much closer viewing for an "Immersive" experience.
John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: 585-477-5325 Cell: 585-781-4036 Fax: 585-722-7243
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Website:
http://www.kodak.com/go/motion
[This message has been edited by John Pytlak (edited May 15, 2003).]